1. Fiend of the Invention
The present invention relates to a method of removing surface defects, such as cracks, on the surface of a steel product designed for rolling, such as a slab. The surface of a raw material for rolling, such as a slab and a steel block, is covered with a thick oxidized membrane and usually has many defects therein, such as, for example, cracks, having a maximum depth of about 10 mm in the surface layer.
When the raw material is rolled, such defects remain on the surface of the rolled product so as to deteriorate the quality of the rolled product.
2. Description of the Prior Art
An attempt has been made to remove such defects by a method of mechanically shaving the surface layer of the slab or the like prior to the rolling operation. However, the conventional method of removing such defects has certain disadvantages, most especially in that there is a need for many steps and the yield is remarkably decreased.
In order to overcome such disadvantages, an apparatus has been proposed for removing these surface defects of a slab by generating an arc between a non-consumable electrode and the surface of the slab in an inert gas or a reducible gas atmosphere, moving the arc by a magnetic field to melt 100% of the surface of the slab along a desirable depth and then quenching it. However, in accordance with this method, an amount of the dissolved gas in the molten surface part is increased to thus change the quality of the surface, and also blow-holes are formed therein, so as to leave a non-uniform surface after the rolling operation has been completed. Accordingly, the conventional methods, while somewhat successful, have not been entirely satisfactory.